What imaging modalities are recommended for diagnosing adrenal insufficiency?

Imaging for Adrenal Insufficiency Diagnosis

Imaging plays essentially no role in the diagnosis of adrenal insufficiency itself, which is a biochemical diagnosis based on cortisol and ACTH levels; however, CT of the adrenal glands is indicated to identify the underlying structural cause once biochemical adrenal insufficiency is confirmed. 1

Primary Diagnostic Approach

The diagnosis of adrenal insufficiency is established through hormonal testing, not imaging 2:

• Early morning (8 AM) serum cortisol, ACTH, and DHEAS measurements are the cornerstone of diagnosis 2
• Primary adrenal insufficiency shows low cortisol (<5 µg/dL), elevated ACTH, and low DHEAS 2
• Secondary adrenal insufficiency demonstrates low-to-intermediate cortisol (5-10 µg/dL) with low or low-normal ACTH and DHEAS 2
• Patients with intermediate cortisol levels require corticotropin stimulation testing (250 µg cosyntropin with cortisol measurement at baseline and 60 minutes) 2

Role of CT Imaging

Once adrenal insufficiency is biochemically confirmed and autoimmune etiology is excluded (negative 21-hydroxylase antibodies), CT of the adrenal glands should be performed as the first-line imaging modality to identify structural causes 1:

• Unenhanced CT is the preferred initial imaging technique to detect calcifications typical of tuberculosis, tumors, hemorrhage, or infiltrative disease 1, 3
• CT can identify adrenal metastases, lymphoma, hemorrhage, or bilateral infiltrative processes 1
• The scan should specifically look for calcifications (suggesting prior tuberculosis), masses, hemorrhage, or atrophic glands 1

When Imaging Is Indicated

Imaging should be pursued in specific clinical scenarios 1:

• Young patients or elderly patients who are 21-hydroxylase antibody negative (autoimmune cause less likely) 1
• Suspected non-autoimmune causes such as infection, hemorrhage, infiltration, or malignancy 1
• Males should be screened for adrenoleukodystrophy with very long-chain fatty acids before imaging, as this X-linked condition presents with adrenal insufficiency 1
• Bilateral adrenal incidentalomas discovered incidentally require assessment for adrenal insufficiency 1

MRI Considerations

MRI has limited utility in diagnosing adrenal insufficiency but may be useful in specific contexts 4:

• Chemical shift MRI can characterize adrenal masses if CT findings are indeterminate 1, 4
• MRI is preferred in pregnant patients, young adults, and children when radiation exposure is a concern 1
• Dynamic enhanced MRI may help differentiate benign from malignant lesions but is not routinely needed for adrenal insufficiency evaluation 1

Nuclear Medicine Imaging

Nuclear medicine studies (MIBG, iodocholesterol scans) are not indicated for diagnosing adrenal insufficiency 1:

• MIBG scintigraphy is specific for pheochromocytoma and paraganglioma, not adrenal insufficiency 1
• These studies evaluate adrenal medulla function, not cortical function 1
• Iodocholesterol scans may detect functional adenomas but do not diagnose insufficiency 1

Common Pitfalls to Avoid

• Do not order imaging before confirming biochemical adrenal insufficiency - the diagnosis is hormonal, not radiological 1, 2
• Do not perform adrenal biopsy for suspected adrenal insufficiency - it provides no diagnostic value and carries risks including hemorrhage and infection 1
• In autoimmune adrenal insufficiency (21-hydroxylase antibody positive), imaging is typically unnecessary as the glands may appear normal or atrophic 1
• Always measure very long-chain fatty acids in males before attributing insufficiency to "idiopathic" causes, as adrenoleukodystrophy is treatable if caught early 1
• In bilateral infiltrative disease, metastases, or hemorrhage, assess for concurrent adrenal insufficiency even if imaging was performed for other reasons 1

Specific Etiologies Identified by CT

CT findings that explain adrenal insufficiency include 1, 3:

• Calcifications: Tuberculosis (most common infectious cause globally) 1
• Bilateral masses: Metastases, lymphoma, or hemorrhage 1, 3
• Infiltrative changes: Amyloidosis, hemochromatosis, or sarcoidosis 1
• Atrophic glands: Long-standing autoimmune destruction 1
• Hemorrhage: Visible as high-density lesions on unenhanced CT 3